Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755382Ab0HJHlB (ORCPT ); Tue, 10 Aug 2010 03:41:01 -0400 Received: from mailout4.w1.samsung.com ([210.118.77.14]:47797 "EHLO mailout4.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753575Ab0HJHkz convert rfc822-to-8bit (ORCPT ); Tue, 10 Aug 2010 03:40:55 -0400 MIME-version: 1.0 Content-type: text/plain; charset=utf-8; format=flowed; delsp=yes Date: Tue, 10 Aug 2010 09:42:31 +0200 From: =?utf-8?B?TWljaGHFgiBOYXphcmV3aWN6?= Subject: Re: [PATCHv2 2/3] lib: vsprintf: optimised put_dec() for 32-bit machines In-reply-to: <201008100615.52510.vda.linux@googlemail.com> To: Michal Nazarewicz , Denys Vlasenko Cc: linux-kernel@vger.kernel.org, "Douglas W. Jones" , Andrew Morton Message-id: Organization: Samsung Electronics Content-transfer-encoding: 8BIT User-Agent: Opera Mail/10.60 (Linux) References: <6f90103dea29739de0f4f0ede3f3da68afe84343.1281295424.git.mina86@mina86.com> <419733287a42072a658f0f74d0b1901132178b75.1281295424.git.mina86@mina86.com> <201008100615.52510.vda.linux@googlemail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3655 Lines: 96 > On Sunday 08 August 2010 21:29, Michal Nazarewicz wrote: >> Compared to previous version: the code is used only if: >> 1. if long long is 64-bit (ie. ULLONG_MAX == 2**64-1), and >> 2. user did not select optimisation for size with Kconfig. On Tue, 10 Aug 2010 06:15:52 +0200, Denys Vlasenko wrote: > I measured the size and it does not seem to make sense > to exclude it on -Os. On x86: > > put_dec_full change: 0x93 -> 0x47 bytes > put_dec change: 0x12c -> 0x137 bytes > > IOW, there is net code size reduction (compared to current kernel, > it may be a slight growth compared to patch 1). > > So, please use the optimized code even for CONFIG_CC_OPTIMIZE_FOR_SIZE. Will do. >> Here are the results (normalised to the fastest/smallest): >> : ARM Atom >> -- Speed ---------------------------------- >> orig_put_dec : 9.333822 2.083110 Original >> mod1_put_dec : 9.282045 1.904564 >> mod2_put_dec : 9.260409 1.910302 >> mod3_put_dec : 9.320053 1.905689 Proposed by previous patch >> mod4_put_dec : 9.297146 1.933971 >> mod5_put_dec : 13.034318 2.434942 >> mod6_put_dec : 1.000000 1.000000 Proposed by this patch >> mod7_put_dec : 1.009574 1.014147 >> mod8_put_dec : 7.226004 1.953460 >> -- Size ----------------------------------- >> orig_put_dec : 1.000000 1.000000 Original >> mod1_put_dec : 1.000000 1.000000 >> mod2_put_dec : 1.361111 1.403226 >> mod3_put_dec : 1.000000 1.000000 Proposed by previous patch >> mod4_put_dec : 1.361111 1.403226 >> mod5_put_dec : 1.000000 1.000000 >> mod6_put_dec : 2.555556 3.508065 Proposed by this patch >> mod7_put_dec : 2.833333 3.911290 >> mod8_put_dec : 2.027778 2.258065 > > I believe these are old results? Size growth is just too big. Hmm... I think those are new results, but I might have messed something up. I'll redo them. >> +#if BITS_PER_LONG != 32 || defined CONFIG_CC_OPTIMIZE_FOR_SIZE || \ >> + ULLONG_MAX != 18446744073709551615ULL > > I think it's better to say "if BITS_PER_LONG > 32 and ULLONG_MAX > 2^64-1", > since it expresses your intent better. Also, add comments explaining > what case you optimize for: Will do. >> +static noinline_for_stack >> +char *put_dec(char *buf, unsigned long long n) >> +{ >> + uint32_t d3, d2, d1, q; >> + >> + if (!n) { >> + *buf++ = '0'; >> + return buf; >> + } > You may as well use the above shortcut for n <= 9, not only for 0. Will do. >> + buf = put_dec_full4(buf, q % 10000); >> + q = q / 10000; >> + >> + d1 = q + 7671 * d3 + 9496 * d2 + 6 * d1; >> + buf = put_dec_full4(buf, d1 % 10000); >> + q = d1 / 10000; > > I experimented with moving division up, before put_dec_full4: > q = d1 / 10000; > buf = put_dec_full4(buf, d1 % 10000); > but gcc appears to be smart emough to do this transformation > itself. But you may still do it for older (dumber) gcc's. I wasn't sure where would be a better place to put this line. I'll follow your advice on this one then. -- Best regards, _ _ | Humble Liege of Serenely Enlightened Majesty of o' \,=./ `o | Computer Science, Michał "mina86" Nazarewicz (o o) +----[mina86*mina86.com]---[mina86*jabber.org]----ooO--(_)--Ooo-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/